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TOPIC: What grit/micron should I have mirror polish?

Re: What grit/micron should I have mirror polish? 2 years 3 weeks ago #4358

  • DavidHamilton2
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There is some interesting and cool science here, but maybe a better definition of mirror like might be a term borrowed from coin collecting (hey, they work with metal, not glass). {You can skip down to the last paragraph if you wish to skip the background}

rare coins absolutely can NOT be polished without destroying it's value. a coins grade relates to the condition it was in the moment the dies struck it. anything that happened after that is damage, The value of a damaged coin is often orders of magnitude below undamaged coins (though honest wear lowers the value but doesn't destroy it).

There are many companies (some of them highly respected) that grade and encapsulate rare coins. coins are rated on a scale of 1 (you can tell it is a dime) to 70 (unobtainable perfection) with a few qualifiers sometimes used after the number. Depending on the coin, the difference between say, a MS65 and a MS 66 grade might be 10, or even 100's of thousands of dollars.

---Read the next two paragraph only if you want to know more about coin grading---

Coins can be graded either Mint State 1-70 (MS1 to MS70) this means the coins were made for commerce, the coins in your pocket probably average MS 45 or so, when you get a brand new new nickle out of a fresh from the mint roll, that is likely a MS 63 or so.

coins can also be Proof's, they "can" be graded PF 1 to PF 70, though the lower grades are rare. Proofs are usually minted for collectors. they are made in small quantities, they use specially prepared blanks and are stamped much slower and with much more pressure so they have much more detail. If a proof is in a low grade it was probably stolen from a collection and spent, more likely, on the rare time a proof got circulated, it will lose it's proof diagnostic and become an MS coin

Proofs are usually mirror finished, but not always. but they are pretty much always specimen strikes


!!were AT info for the KNIFE guys now!!

SORRY IT TOOK SO LONG TO GET HERE, BUT THIS IS WHAT THE COIN GUYS SAY


An official grade qualifier from the most respected grading company is DMPL That qualifier can add Thousands to the price of a coin. It stands for Deep Mirror Proof Like.

the coin that earns that DMPL is not a proof, it is proof like, but by definition, news print can be read from 4 inches away under good (but not direct light).



____________________________end of the line

So, I propose knife nuts follow coin collectors. If we can read news print 4 inches away, it is a mirror. discuss as you wish
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Re: What grit/micron should I have mirror polish? 2 years 3 weeks ago #4367

  • PhilipPasteur
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oxforddictionaries.com/definition/english/mirror

noun
• a surface, typically of glass coated with a metal amalgam, which reflects a clear image: he checked his appearance in the mirror
• a thing regarded as accurately representing something else: the stage is supposed to be the mirror of life
www.thefreedictionary.com/mirror
mir•ror (m r r)
n.
1. A surface capable of reflecting sufficient undiffused light to form an image of an object placed in front of it. Also called looking glass.
2. Something that faithfully reflects or gives a true picture of something else.



dictionary.reference.com/browse/mirror

mir•ror

noun
1.
a reflecting surface, originally of polished metal but now usually of glass with a silvery, metallic, or amalgam backing.
2.
such a surface set into a frame, attached to a handle, etc., for use in viewing oneself or as an ornament.
3.
any reflecting surface, as the surface of calm water under certain lighting conditions.
4.
Optics . a surface that is either plane, concave, or convex and that reflects rays of light.
5.
something that gives a minutely faithful representation, image, or idea of something else: Gershwin's music was a mirror of its time.

1. mirror(noun)
polished surface that forms images by reflecting light
unattributed supposedly from Princeton's WordNet

Ok, If you read the dictionary definitions of what a mirror is above it is easy to see how hard it will be to come to a consensus on what a mirror edge is. The definitions are all pretty vague and subjective, to say the least. I can see that Anthony did a good job in showing me that my personal perception of what a mirror should be is a bit limited. Of course the idea of setting some kind of standard is in itself limiting. The hard part is to get people to agree with and use the standard. We could use the ISO or ANSI standards for surface finish, but then the measurements to show compliance is a problem.

I think that the idea of reading text of a specific size at a specific distance may be as good as we can get people to use. It is a simple concept and easy to perform. Unfortunately it will not show the difference between a 2K grit reflection and one done with submicron abrasives. I am sure that both will pass this test but will look completely different. It may be like the difference between the 65 and 68 rated coin, you would need to submit the blade to some kind of certified expert and let then subjectively rate them. Of course this will not happen.

Anyway, it whas been a good discussion and I learned quite a bit in doing research and reading other posts.

So, who else would be in for definng a minimal mirror edge to be one where newsprint can be read at 4 inches under "good" (whatever that means :) but not direct light??

Phil
Phil

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Last Edit: 2 years 3 weeks ago by PhilipPasteur. Reason: remove html code
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Re: What grit/micron should I have mirror polish? 2 years 3 weeks ago #4370

  • StevenPinson
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I can only write, I cannot read. :silly:
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Re: What grit/micron should I have mirror polish? 2 years 3 weeks ago #4379

  • AnthonyYan
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Here are three possible tests for "mirror finish":

(1) Reading newsprint/fine-print in the reflection at some reasonable distance (4 inches? 6 inches?), and no visible "haze" on the surface.
(2) Laser-pointer test: stellafane.org/tm/atm/polish/polish.html#Polished_Out
(3) Microscope test: No visible scratches under magnification. (100x? 200x?)

Any one of these seem reasonable to me. I think (1) is the most informal and least stringent. But between (2) and (3) I don't know which is more stringent (and it might depend on magnification and microscope quality, as well as depend somewhat on laser wavelength).

Sincerely,
--Lagrangian

P.S. Apparently,for the laser-test, amateur telescope makers tend to recommend red lasers for the test. For details, see stellafane.org/tm/atm/test/quality.html#polish
Last Edit: 2 years 3 weeks ago by AnthonyYan. Reason: Added P.S.
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Re: What grit/micron should I have mirror polish? 2 years 3 weeks ago #4380

  • PhilipPasteur
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StevenPinson wrote:
I can only write, I cannot read. :silly:

You can count belly button lint fibers at 4 inches...

:)
Phil

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I miss you Buddy!
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Re: What grit/micron should I have mirror polish? 2 years 3 weeks ago #4381

  • PhilipPasteur
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I think number one and three would be good criteria. I am not sure how number two would be applicable to polished steel.
Here is a quote from the article that is linked:

"But you should see NO reflection from the front surface. Yes, that is correct, a fully polished mirror will have essentially no reflection (that most people can discern) -- it appears the polished surface is not there at all! If your mirror in not fully polished, the "rough" surface will scatter some light to the side, which you will see as a front surface reflection".

So they are looking for scatter off of the polished surface of the mirror contrasted to a good reflection from the unpolished rear of the mirror. I guess we could look at how accuratelly the laser is being reflected from the edge. Rather than looking at the reflected laser (not god for the eyes) we could focus the reflection on a piece of white paper to examine the image.

Anyway, some good thoughts !!

Phil



AnthonyYan wrote:
Here are three possible tests for "mirror finish":

(1) Reading newsprint/fine-print in the reflection at some reasonable distance (4 inches? 6 inches?), and no visible "haze" on the surface.
(2) Laser-pointer test: stellafane.org/tm/atm/polish/polish.html#Polished_Out
(3) Microscope test: No visible scratches under magnification. (100x? 200x?)

Any one of these seem reasonable to me. I think (1) is the most informal and least stringent. But between (2) and (3) I don't know which is more stringent (and it might depend on magnification and microscope quality, as well as depend somewhat on laser wavelength).

Sincerely,
--Lagrangian

P.S. Apparently,for the laser-test, amateur telescope makers tend to recommend red lasers for the test. For details, see stellafane.org/tm/atm/test/quality.html#polish
Phil

MAX 2001-2013
Hoping there is that bridge!
I miss you Buddy!
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